Note For complete syntax and usage information for the switch commands used in this chapter, look at the Cisco Catalyst 4500 Series Switch Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/hw/switches/ps4324/index.html

If the command is not found in the Catalyst 4500 Command Reference, it is located in the larger Cisco IOS library. Refer to the Catalyst 4500 Series Switch Cisco IOS Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/ps6350/index.html

Checking Module Status

The Catalyst 4500 series switch is a multimodule system. You can see which modules are installed, as well as the MAC address ranges and version numbers for each module, by using the show module command. You can use the [mod_num] argument to specify a particular module number to see detailed information on that module.

This example shows how to check module status for all modules on your switch:

Checking Interfaces Status

You can view summary or detailed information on the switch ports using the show interfaces status command. To see summary information on all ports on the switch, enter the show interfaces status command with no arguments. Specify a particular module number to see information on the ports on that module only. Enter both the module number and the port number to see detailed information about the specified port.

To apply configuration commands to a particular port, you must specify the appropriate logical module. For more information, see the "Checking Module Status" section.

This example shows how to display the status of all interfaces on a Catalyst 4500 series switch, including transceivers. Output of this command displays "Unapproved GBIC" for non-Cisco transceivers:

Switch#show interfaces status

Port Name Status Vlan Duplex Speed Type

Gi1/1 notconnect 1 auto auto No Gbic

Gi1/2 notconnect 1 auto auto No Gbic

Gi5/1 notconnect 1 auto auto 10/100/1000-TX

Gi5/2 notconnect 1 auto auto 10/100/1000-TX

Gi5/3 notconnect 1 auto auto 10/100/1000-TX

Gi5/4 notconnect 1 auto auto 10/100/1000-TX

Fa6/1 connected 1 a-full a-100 10/100BaseTX

Fa6/2 connected 2 a-full a-100 10/100BaseTX

Fa6/3 notconnect 1 auto auto 10/100BaseTX

Fa6/4 notconnect 1 auto auto 10/100BaseTX

Switch#

This example shows how to display the status of interfaces in error-disabled state:

Switch# show interfaces status err-disabled

Port Name Status Reason

Fa9/4 err-disabled link-flap

informational error message when the timer expires on a cause

--------------------------------------------------------------

5d04h:%PM-SP-4-ERR_RECOVER:Attempting to recover from link-flap err-disable state on Fa9/4

Switch#

Displaying MAC Addresses

In addition to displaying the MAC address range for a module using the show module command, you can display the MAC address table information of a specific MAC address or a specific interface in the switch using the show mac-address-table address and show mac-address-table interface commands.

This example shows how to display MAC address table information for a specific MAC address:

Checking Cable Status Using Time Domain Reflectometer

You can use the Time Domain Reflectometer (TDR) feature to determine if cabling is at fault when you cannot establish a link.

Note This test is especially important when replacing an existing switch, upgrading to Gigabit Ethernet, or installing new cable plants.

Overview

With TDR, you can check the status of copper cables on the 48-port 10/100/1000 BASE-T modules for the Catalyst 4500 series switch (WS-X4548-GB-RJ45, WS-X4548-GB-RJ45V, WS-X4524-GB-RJ45V, WS-X4013+TS, WS-C4948, and WS-C4948-10GE). TDR detects a cable fault by sending a signal through the cable and reading the signal that is reflected back. All or part of the signal can be reflected back either by cable defects or by the end of the cable.

Note There are four pairs of standard category 5 cable. Each pair can assume one of the following states: open (not connected), broken, shorted, or terminated. The TDR test detects all four states and displays the first three as "Fault" conditions, and displays the fourth as "Terminated." Although the CLI output is shown, the cable length is shown only if the state is "Faulty."

This example shows the message that displays when the TDR test is not supported on a module:

Switch# test cable-diagnostics tdr int gi2/1

00:03:15:%C4K_IOSDIAGMAN-4-TESTNOTSUPPORTEDONMODULE: Online cable

diag tdr test is not supported on this module

Switch#

This example shows how to display TDR test results for a port:

Switch# show cable-diagnostics tdr interface gi4/13

Interface Speed Local pair Cable length Remote channel Status

Gi4/13 0Mbps 1-2 102 +-2m Unknown Fault

3-6 100 +-2m Unknown Fault

4-5 102 +-2m Unknown Fault

7-8 102 +-2m Unknown Fault

Note This command will be deprecated in future releases of Cisco IOS software. Please use the diagnostic start and the show diagnostic result commands to run the TDR test and display the test results.

Note TDR is a port test; the port can not handle traffic for the duration of the test (generally, 1 minute).

Guidelines

The following guidelines apply to the use of TDR:

•If you connect a port undergoing a TDR test to an Auto-MDIX enabled port, the TDR result might be invalid. In those instances, the port on the WS-X4148-RJ45V should be administratively down before the start of the TDR test.

•If you connect a port undergoing a TDR test to a 100BASE-T port such as that on the WS-X4148-RJ45V, the unused pairs (4-5 and 7-8) will be reported as faulty because the remote end does not terminate these pairs.

•Do not change the port configuration while the TDR test is running.

•Due to cable characteristics, you should run the TDR test multiple times to get accurate results.

•Do not change port status (i.e. remove the cable at the near or far end), as this might make the results inaccurate.

Using Telnet

You can access the switch command-line interface (CLI) using Telnet. In addition, you can use Telnet from the switch to access other devices in the network. You can have up to eight simultaneous Telnet sessions.

Using Ping

Understanding How Ping Works

You can use the ping command to verify connectivity to remote hosts. If you attempt to ping a host in a different IP subnetwork, you must define a static route to the network or configure a router to route between those subnets.

The ping command is configurable from normal executive and privileged EXEC mode. Ping returns one of the following responses:

Using IP Traceroute

Understanding How IP Traceroute Works

You can use IP traceroute to identify the path that packets take through the network on a hop-by-hop basis. The command output displays all network layer (Layer 3) devices, such as routers, that the traffic passes through on the way to the destination.

Layer 2 switches can participate as the source or destination of the trace command but will not appear as a hop in the trace command output.

The trace command uses the Time To Live (TTL) field in the IP header to cause routers and servers to generate specific return messages. Traceroute starts by sending a User Datagram Protocol (UDP) datagram to the destination host with the TTL field set to 1. If a router finds a TTL value of 1 or 0, it drops the datagram and sends back an Internet Control Message Protocol (ICMP) Time-Exceeded message to the sender. Traceroute determines the address of the first hop by examining the source address field of the ICMP Time-Exceeded message.

To identify the next hop, traceroute sends a UDP packet with a TTL value of 2. The first router decrements the TTL field by 1 and sends the datagram to the next router. The second router sees a TTL value of 1, discards the datagram, and returns the Time-Exceeded message to the source. This process continues until the TTL is incremented to a value large enough for the datagram to reach the destination host or until the maximum TTL is reached.

To determine when a datagram reaches its destination, traceroute sets the UDP destination port in the datagram to a very large value that the destination host is unlikely to be using. When a host receives a datagram with an unrecognized port number, it sends an ICMP Port Unreachable error message to the source. The Port Unreachable error message indicates to traceroute that the destination has been reached.

Running IP Traceroute

To trace the path that packets take through the network, perform this task in EXEC or privileged EXEC mode:

Command

Purpose

Switch# trace [protocol] [destination]

Runs IP traceroute to trace the path that packets take through the network.

This example shows use the trace command to display the route a packet takes through the network to reach its destination:

Using Layer 2 Traceroute

The Layer 2 traceroute feature allows the switch to identify the physical path that a packet takes from a source device to a destination device. Layer 2 traceroute supports only unicast source and destination MAC addresses. It determines the path by using the MAC address tables of the switches in the path. When the switch detects a device in the path that does not support Layer 2 traceroute, the switch continues to send Layer 2 trace queries and lets them time out.

If you want the switch to trace the path from a host on a source device to a host on a destination device, the switch can identify only the path from the source device to the destination device. It cannot identify the path that a packet takes from source host to the source device or from the destination device to the destination host.

•All switches in the physical path must have IP connectivity. When a switch is reachable from another switch, you can test connectivity by using the ping command in privileged EXEC mode.

•The maximum number of hops identified in the path is ten.

•You can enter the traceroute mac or the traceroute mac ip command in privileged EXEC mode on a switch that is not in the physical path from the source device to the destination device. All switches in the path must be reachable from this switch.

•The traceroute mac command output shows the Layer 2 path only when the specified source and destination MAC addresses belong to the same VLAN. If you specify source and destination MAC addresses that belong to different VLANs, the Layer 2 path is not identified, and an error message appears.

•If you specify a multicast source or destination MAC address, the path is not identified, and an error message appears.

•If the source or destination MAC address belongs to multiple VLANs, you must specify the VLAN to which both the source and destination MAC addresses belong. If the VLAN is not specified, the path is not identified, and an error message appears.

•The traceroute mac ip command output shows the Layer 2 path when the specified source and destination IP addresses belong to the same subnet. When you specify the IP addresses, the switch uses Address Resolution Protocol (ARP) to associate the IP address with the corresponding MAC address and the VLAN ID.

–If an ARP entry exists for the specified IP address, the switch uses the associated MAC address and identifies the physical path.

–If an ARP entry does not exist, the switch sends an ARP query and tries to resolve the IP address. If the IP address is not resolved, the path is not identified, and an error message appears.

•When multiple devices are attached to one port through hubs (for example, multiple CDP neighbors are detected on a port), the Layer 2 traceroute feature is not supported. When more than one CDP neighbor is detected on a port, the Layer 2 path is not identified, and an error message appears.

•This feature is not supported in Token Ring VLANs.

Running Layer 2 Traceroute

To display the physical path that a packet takes from a source device to a destination device, perform either one of these tasks in privileged EXEC mode:

Command

Purpose

Switch# traceroute mac {source-mac-address} {destination-mac-address}

Runs Layer 2 traceroute to trace the path that packets take through the network.

Runs IP traceroute to trace the path that packets take through the network.

These examples show how to use the traceroute mac and traceroute mac ip commands to display the physical path a packet takes through the network to reach its destination:

Switch# traceroute mac 0000.0201.0601 0000.0201.0201

Source 0000.0201.0601 found on con6[WS-C2950G-24-EI] (2.2.6.6)

con6 (2.2.6.6) :Fa0/1 => Fa0/3

con5 (2.2.5.5 ) : Fa0/3 => Gi0/1

con1 (2.2.1.1 ) : Gi0/1 => Gi0/2

con2 (2.2.2.2 ) : Gi0/2 => Fa0/1

Destination 0000.0201.0201 found on con2[WS-C3550-24] (2.2.2.2)

Layer 2 trace completed

Switch#

Switch# traceroute mac ip 2.2.66.66 2.2.22.22 detail

Translating IP to mac .....

2.2.66.66 => 0000.0201.0601

2.2.22.22 => 0000.0201.0201

Source 0000.0201.0601 found on con6[WS-C2950G-24-EI] (2.2.6.6)

con6 / WS-C2950G-24-EI / 2.2.6.6 :

Fa0/1 [auto, auto] => Fa0/3 [auto, auto]

con5 / WS-C2950G-24-EI / 2.2.5.5 :

Fa0/3 [auto, auto] => Gi0/1 [auto, auto]

con1 / WS-C3550-12G / 2.2.1.1 :

Gi0/1 [auto, auto] => Gi0/2 [auto, auto]

con2 / WS-C3550-24 / 2.2.2.2 :

Gi0/2 [auto, auto] => Fa0/1 [auto, auto]

Destination 0000.0201.0201 found on con2[WS-C3550-24] (2.2.2.2)

Layer 2 trace completed.

Switch#

Configuring ICMP

Internet Control Message Protocol (ICMP) provides many services that control and manage IP connections. ICMP messages are sent by routers or access servers to hosts or other routers when a problem is discovered with the Internet header. For detailed information on ICMP, refer to RFC 792.

Enabling ICMP Protocol Unreachable Messages

If the Cisco IOS software receives a nonbroadcast packet that uses an unknown protocol, it sends an ICMP Protocol Unreachable message back to the source.

Similarly, if the software receives a packet that it is unable to deliver to the ultimate destination because it knows of no route to the destination address, it sends an ICMP Host Unreachable message to the source. This feature is enabled by default.

To enable the generation of ICMP Protocol Unreachable and Host Unreachable messages, enter the following command in interface configuration mode:

Command

Purpose

Switch (config-if)# [no] ip unreachables

Enables ICMP destination unreachable messages.

Use the no keyword to disable the ICMP destination unreachable messages.

Caution If you issue the
no ip unreachables command, you will break "path MTU discovery" functionality. Routers in the middle of the network might be forced to fragment packets.

To limit the rate that Internet Control Message Protocol (ICMP) destination unreachable messages are generated, perform this task:

Command

Purpose

Switch (config)# [no] ip icmp rate-limit
unreachable [df]milliseconds

Limits the rate that ICMP destination messages are generated.

Use the no keyword to remove the rate limit and reduce the CPU usage.

Enabling ICMP Redirect Messages

Data routes are sometimes less than optimal. For example, it is possible for the router to be forced to resend a packet through the same interface on which it was received. If this occurs, the Cisco IOS software sends an ICMP Redirect message to the originator of the packet telling the originator that the router is on a subnet directly connected to the receiving device, and that it must forward the packet to another system on the same subnet. The software sends an ICMP Redirect message to the packet's originator because the originating host presumably could have sent that packet to the next hop without involving this device at all. The Redirect message instructs the sender to remove the receiving device from the route and substitute a specified device representing a more direct path. This feature is enabled by default.

To enable the sending of ICMP Redirect messages if the Cisco IOS software is forced to resend a packet through the same interface on which it was received, enter the following command in interface configuration mode:

Command

Purpose

Switch (config-if)# [no] ip redirects

Enables ICMP Redirect messages.

Use the no keyword to disable the ICMP Redirect messages and reduce CPU usage.

Enabling ICMP Mask Reply Messages

Occasionally, network devices must know the subnet mask for a particular subnetwork in the internetwork. To obtain this information, devices can send ICMP Mask Request messages. These messages are responded to by ICMP Mask Reply messages from devices that have the requested information. The Cisco IOS software can respond to ICMP Mask Request messages if the ICMP Mask Reply function is enabled.

To have the Cisco IOS software respond to ICMP mask requests by sending ICMP Mask Reply messages, perform this task: